As well known, an air conditioner for a vehicle compresses a gas refrigerant by a compressor driven by a power source, such as an engine, for driving a vehicle, condenses the gas refrigerant, which has been heated to a high temperature and compressed with a high pressure, by a condenser, and turns the gas refrigerant into a low-temperature and low-pressure liquid refrigerant by performing decompression therefor by expansion means, and thereafter, evaporates the liquid refrigerant by an evaporator, thereby cooling an air-conditioning wind blown out into a vehicle cabin. The refrigerant evaporated by the evaporator returns to the compressor, and then, the above-described cycle is repeated.
In recent years, in response to a request for fuel consumption improvement, a variable capacity compressor provided with an electronic operation control valve (hereinafter, referred to as an ECV) controlled by an electric signal given from the outside has come to be used. In an air conditioner provided with this type of compressor, a target temperature of air to be blown out from the evaporator is calculated based on a set temperature set by a passenger, an actual temperature of the blown-out air is detected by a sensor, a duty ratio of the ECV is calculated based on the target temperature and the actual temperature, and based on the duty ratio, a discharged volume of the refrigerant from the compressor is controlled. Hence, the discharged volume of the refrigerant from the compressor can be controlled precisely, and accordingly, the fuel consumption improvement can be achieved.
Moreover, recently, in response to that the request for the fuel consumption improvement has been further being increased, a control method has also been sometimes adopted, in which an air conditioner computer for controlling the air conditioner and an engine computer make communication with each other, a duty signal capable of reducing power of the compressor while ensuring comfortableness is calculated in response to a running state, an engine load, and the like, and the duty signal is given to the ECV in an interruptive manner.
However, in the above-described conventional technology, there has been a case where it is difficult to calculate an appropriate duty signal, and where the comfortableness and the fuel consumption improvement cannot be made sufficiently compatible with each other.